xlib plugin is dead (for Qt5)

[Rick Stockton]

This is an FYI, I don't speak for Qt-Project (I'm not an Approver or 
Maintainer, just a VERY occasional contributor.)

In a merge earlier today, Qt-Project removed the xlib support code form 
Qt5. (I was not the Approver, but I did vote "+1" on the change). For 
X11 environments, xcb will be it's replacement. Wayland is also a 
"primary" platform, but IMO not completely ready for prime-time use as a 
Qt back-end. (QT requires an SHA1 level of Wayland which is somewhat 
old, slightly buggy, slightly less efficient than current Wayland Git, 
which also adds a few new features over the level now required by 
Qt5-Wayland.)

xcb also has some performance enhancements init's current Git version, 
compared to the recent official Releases (1.8.0 and 1.8.1). If you build 
Qt against a Released Version, (e.g. 1.8.1), Qt "configure" will include 
a line in it's Build Summary, saying that "xcb support is limited (old 
version)." This message is with respect to those recent changes, which 
allow for more efficient painting.

Qt-Project is still looking for a maintainer of Widgets- and if someone 
doesn't volunteer, support for "traditional" Widgets obviously becomes 
very questionable.